Multidimensional coding, or turbo coding, and associated iterative decoding methods have increasingly important application as data transmission services grow in sophistication. For example, next generation wireless communications systems currently under development are expected to support internet-based services, such as e-mail and web browsing. It has been proposed for at least some of these wireless communications systems to utilize turbo coding for the higher speed data transmission of the system.
A turbo decoder decodes an encoded signal by recursively processing frames of the encoded signal using more than one iteration through the decoder, as described, for example, by Berrou in "New Shannon Limit Error-correcting and Decoding: Turbo-codes (1)" Proceedings ICC 1993, pp. 1064-1070, and by Berrou and Glavieux in "Turbo-codes: General Principles and Applications," Audio and Video Digital Radio Broadcasting Systems and Techniques, 1993, pp. 215-226.
Several schemes have been presented in the literature for improving the performance of iterative decoders. U.S. Pat. No. 5,761,248, "Method and Arrangement for Determining an Adaptive Abort Criterion in Iterative Decoding of Multi-Dimensionally Coded Information," Hagenover, et al., discloses a method and apparatus for comparing a weighted decision on a soft output of a substep of iterative decoding to a weighted decision on a soft output and a combination of previous subsets of iterating and aborting the iterative decoding dependent on the comparison result. The publication, Variable Latency Turbo Codes for Wireless Multimedia Applications," by C. Valenti and D. Woerner, Proceedings of International Symposium on Turbo Codes and Related Topics, Brest, France, September 1997, pp. 216-219, disclosed the use of interleavers of variable sizes to achieve different quality of service, QoS, requirements.
Each of the above methods has its drawbacks. Using the first approach, there is no adaptive QoS consideration. With the second approach, using different interleavers for QoS may be difficult due to incompatibility with specifications of transmission frames per data rate. It also requires both the transmitter and receiver to change interleavers frequently, which is undesirable.